NAME
Apache::Handlers
SYNOPSIS
In code:
use Apache::Handlers qw(CLEANUP);
our $global;
my $session : PerlCleanupHandler;
CLEANUP {
our $global = undef;
};
In httpd.conf:
PerlModule Apache::Handlers
PerlChildInitHandler Apache::Handlers
PerlPostReadRequestHandler Apache::Handlers
Apache::Handlers -> reset;
DESCRIPTION
"Apache::Handlers" provides two different methods of declaring when code
snippets should be run during the Apache request phase.
The code defined with the constructs provided by this module do not
directly affect the success or failure of the request. Thus, this module
does not provide a replacement for content, access, or other handlers.
The code is executed in the order it is encountered except for
"CHILDEXIT", "CLEANUP", "PerlChildExitHandler", and "PerlCleanupHandler"
code. These are executed in the reverse order, similar to the pairing of
"BEGIN" and "END" blocks.
The block construct or attribute must be run before the phase it refers
to. Otherwise, it won't be run in that phase. The phases are run in the
following order:
CHILDINIT TRANS HEADERPARSER ACCESS AUTHEN AUTHZ TYPE FIXUP CONTENT LOG
CLEANUP CHILDEXIT
The RESTART phase is not an actual Apache request phase and has no
effect after the server has started. It is used to define code that
should run during the server startup phase when Apache reads the server
configuration the second time or is gracefully (or not so gracefully)
restarted. It should be used to clean up so the second configuration
process won't duplicate information or cause errors.
If this module is called during the ChildInit phase, then it will only
call that code associated with CHILDINIT blocks. Otherwise, the
CHILDINIT code will be run at the first opportunity (basically, the
first request made of the child process). Thus the two Perl*Handler
configuration directives in the Synopsis.
Running without mod_perl
When developing outside mod_perl, all code associated with CHILDINIT,
TRANS, HEADERPARSER, ACCESS, AUTHEN, AUTHZ, TYPE, FIXUP, and CONTENT is
run in an "INIT" block. All code associated with LOG, CLEANUP, and
CHILDEXIT is run in an "END" block.
Block Constructs
The following allow for blocks of code to be run at the specified phase.
Note that these are subroutines taking a single code reference argument
and thus require a terminating semi-colon (;). They are named to be like
the BEGIN, END, etc., constructs in Perl, though they are not quite at
the same level in the language.
If the code is seen and handled before Apache has handled a request, it
will be run for each request. Otherwise, it is pushed on the handler
stack, run, and then removed at the end of the request.
These are named the same as the Apache/mod_perl configuration directives
except the "Perl" and "Handler" strings have been removed and the
remainder has been capitalized.
ACCESS
AUTHEN
AUTHZ
CHILDEXIT
CHILDINIT
CLEANUP
CONTENT
FIXUP
HEADERPARSER
LOG
POSTREADREQUEST
RESTART
TRANS
TYPE
Attributes
If Attribute::Handlers is available, then the following attributes are
available (N.B.: Attribute::Handlers requires Perl 5.6.0). These are
named the same as the Apache/mod_perl configuration directives.
If the attribute argument is a constant value (non-CODE reference), then
the variable is assigned that value. Otherwise, it is assigned the value
that the CODE reference returns.
If the attribute is being applied to a subroutine, then that subroutine
is called during that phase. For example, the following two snippets
result in the same code being run at the same time.
my $something = sub : PerlChildExitHandler {
print "We did it!\n";
};
sub something : PerlChildExitHandler {
print "We did it!\n";
};
When an attribute is applied to a subroutine, the argument is ignored.
When the attribute argument is itself a CODE reference, the referent
(the variable the attribute applies to) is passed as a reference:
my $global : PerlChildInitHandler(sub { print "global: $$_[0]\n" });
This will print the value of $global and set it equal to 1 (or the value
of the print statement).
PerlAccessHandler
PerlAuthenHandler
PerlAuthzHandler
PerlChildInitHandler
PerlChildExitHandler
PerlCleanupHandler
PerlFixupHandler
PerlHandler
PerlHeaderParserHandler
PerlLogHandler
PerlPostReadRequestHandler
PerlRestartHandler
PerlTransHandler
PerlTypeHandler
Other Methods
dump
This will dump the current set of code references and return the
string. This uses Data::Dumper.
reset
This will clear out all previously set code. This should only be
used in the "startup.pl" or equivalent so that code doesn't get run
twice during a request (when it should only be run once). This will
also run any RESET blocks that have been defined.
run_phase
Given a list of phases (using the names for the block constructs
above), this will run through the code for that phase, "die"ing
(outside mod_perl) or logging (if in mod_perl) if there is an error.
For example,
run_phase( qw: CONTENT LOG CLEANUP : );
will run any code associated with the CONTENT, LOG, and CLEANUP
phases.
CAVEATS
Caveats are things that at first glance might be bugs, but end up
potentially useful. So I am going to make this section into a kind of
cookbook for non-obvious uses for these potential bugs.
Authentication and Authorization
Be aware that these two phases only run if Apache has reason to believe
they are needed. This can be a bit handy since the following snippet
should tell you if the authentication phase was run. Of course, if an
authentication handler runs before this and returns OK, then this may
not run.
my $authentication_ran : PerlTransHandler(0) PerlAuthenHandler(1);
LOG {
if($authentication_ran) {
# log something special
}
};
Errors
If code causes an error (such that an eval would set $@), then the
request will throw a SERVER_ERROR and write $@ to either STDERR (if not
in mod_perl and there is no "die" handler, such as the Error module) or
to the Apache error log with a log level of debug.
"Use"ing modules
Any of the block constructs or attributes provided by this module that
are used in the body of a module that is brought in via the "use"
keyword will be considered to take place before the child is spawned.
This means that any code designated to run during a particular phase
will be run at the appropriate time as if the module had been loaded
during the server startup.
Modules can now rest assured that using a CLEANUP block in their file
will mean that code is run at the end of every request, even if the
module was loaded in the child process and not during server startup.
This is done by looking for code run during the BEGIN phase.
BUGS
Unlike caveats, bugs are features that are undesirable and/or get in the
way of doing something useful. I'm sure there are some. Please let me
know when you find them.
Security
There is no way (currently) to limit registration of code for later
processing during a particular phase. Ideas are welcome for how this
should be designed.
SEE ALSO
the Apache manpage, the Attribute::Handlers manpage, the Data::Dumper
manpage.
AUTHOR
James G. Smith
COPYRIGHT
Copyright (C) 2002 Texas A&M University. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.